A high-quality stove gas burner typically can produce a relatively large main flame and a smaller warming flame. The latter is normally set such that it cannot exceed a certain size, so that it can be used for simmering or warming but is not really powerful enough for most cooking procedures. The main flame is produced from nozzles that have an overall flow cross section that is much greater than the nozzles forming the warming flame. Typically the warming flame produces about 20% to 25% as much heat as the main flame.
In some systems the warming flame is centered in the burner and in this case it can be even smaller, between 10% and 12% of the overall burner capacity. While this is very handy for most applications, the centered position of this flame creates a hot spot in the center of the cooking utensil sitting on the burner, and in fact food can be burnt because of this concentrated location even in spite of the small size of the flame. Another disadvantage with this system is that a separate igniter must often be provided for the central flame, adding to the cost of the burner, and in general such a dual-flame burner can be quite complex.